Solid waste materials of the type typified by municipal solid waste traditionally have presented problems of disposal. These disposal difficulties have become increasingly critical as populations have expanded and as the per capita production of solid waste has increased. In addition to using waste as a source of fuel or compost, industrial and home refuse or municipal solid waste (MSW) typically comprises several components or fractions which are worth reclaiming. In particular, glass, ferrous and non-ferrous metals, plastic, and paper components are sufficiently valuable to justify their separation from composite MSW. Conventionally, such solid waste has been disposed of by incineration and/or landfill. With the present concern over problems associated with the protection of the environment and because of scarcity of landfill space and governmental regulations, both of these traditional techniques of disposal have become undesirable. Further, separation systems, to remain efficient, must be capable of having a reasonably high throughput rate for the material processed and since MSW varies from one area to the next, and between collections, the separation system must also be capable of handling materials which vary widely in nature and composition. To the present, the throughput rates of conventional systems have not been adequately high enough to derive efficiencies permitting the use of equipment in municipalities of small or medium size. However, because of the ever-increasing rigid requirements for carrying out waste treatment and because of the increasing scarcity of landfill space, some technique must be found to effectively increase such output rates.
To achieve the efficient separation of more valuable fractions of MSW and to derive a marketable compost or refuse derived fuel product, a waste treatment process should be carried out wherein raw MSW is passed through a variety of reduction, separation, and related treatment stages. These stages serve to remove inorganic components such as metals, glass, and plastics from the organic component of the MSW. The segregated or separated by-product materials, such as ferrous and non-ferrous metals, glass, and plastic increasingly are becoming valuable resources worthy of the expenditure of capital for effective separation equipment. Of course, the quality and resultant value of compost by-product is also dependent upon the corresponding quality of separation, the presence of plastics, glass, or other foreign particles being undesirable or unacceptable for most commercial applications.
Disregarding curbside recycling, a broad variety of separation techniques have been known to industry. Among those, both manual and automatic techniques have been used. The manual technique that generally involves human pickers usually is not cost effective nor desirable. The automatic techniques which rely on the fraction size for sortation by a grizzly or the magnetic characteristics of the fraction or the density of the fraction for air separation have generally not been employed by industry in such a manner as to eliminate the extensive need of human pickers to further separate MSW into the various fractions where air separation techniques have been applied to municipal waste separation. Designers have found that achieving high quality separation within reasonable cost limits proves to be an elusive goal. Since municipal waste varies widely in geographical as well as daily make-up and consistency, a uniform product is not available for separation treatment. Therefore, any separation system involving the sortation of solid waste must be capable of handling a wide variation of waste components.